Federighi reiterated the new features at Tuesday's event. A 13-inch MacBook Air with Mavericks gets up to an hour more of Web browsing and up to 1.5 hours more iTunes movie playback, he said.

He also explained how the system adjusts its memory based on the task. This allows for optimal quality when you're running a graphics-heavy program -- and speed when you're not. He also highlighted the iBook app, in which photos and videos can pop out of a textbook, and an iCloud keychain, which syncs payment information for online purchases.

CNET's Jason Parker said in June that the OS is faster and easier to use, and apps have a cleaner look. See his First Take here.